As someone about 75% done with a DKC3 re-playthrough, I think I do have to echo the content creator Geek Critique's (more recent) general thoughts on it. The biggest flaw of it isn't the more gimmicked levels, Kiddy, the lack of DK/Diddy, or even certain emphases in aesthetic. It's the fact that the initial two worlds while fine and even charming in some ways, don't feel like they do justice the more interesting and explorative aspects of the game. Lake Orangatanga & Kremwood Forest are serviceable worlds, and the individual levels are solid enough, but it doesn't really feel like anything really pops until Cotton Top Cove and Mekanos.
Kongo Jungle/Monkey Mines benefited from being visually striking settings while Gangplank Galleon/Crocodile Cauldron pulled either strong off kinetic stage design or really strong aesthetic levels themselves. The first two of DKC3 by contrast almost feel a little too cozy with the lakefront, mill, riverbank, and woods backdrops all working as comfortable environments, just ones that really don't stand out that much. Same with the gimmicks for stages themselves which are all fine and don't feel off while also not really grabbing players with particularly exciting level concepts, Barrel Shield Bust Up aside.
I suppose in some fashion it could be argued they work in easing the player into the Northern Kremisphere region overall and that there is a logic in not playing DKC3's hand too early. For me though as someone that likes of the sense the Kongs going into the unknown and theme of weird experiments being done to mooks/baddies, that identity feels far better serviced by the rest of the game. It almost as if it feels like a basic Donkey Kong Country sequel in the first 25% of the experience, but only really becomes Dixie Kong's Double Trouble after that.